Method and installation for variable power gasification of combustible materials

ABSTRACT

The gasification process according to the invention involves an installation comprising a treatment chamber in which the materials to be treated pass successively through a drying/pyrolysis zone of variable dimensions in which a pyrolysis gas extraction takes place, then through a gasification zone of variable dimensions in which a syngas extraction takes place. The pyrolysis gas is injected into the roof of the treatment chamber ( 8 ) with an oxidizing gas, so as to generate an exothermic oxidation reaction provides the energy necessary for the pyrolysis and gasification reactions. The dimensions and/or the position of the drying/pyrolysis and gasification zones are controlled as a function of the amounts of material to be treated introduced into the treatment chamber ( 8 ), their nature and/or energy requirements.

The present invention relates to a method for variable power gasification of products such as biomass and organic byproducts (plants, animals, domestic refuse, sewage sludges), it being understood that:

-   -   By gasification, is meant a thermochemical method for converting         a solid fuel into a gas fuel. This is an incomplete combustion         since it should result in combustible chemical products.     -   By combustion, is meant an exothermic chemical reaction with         rapid oxidation of a fuel.     -   By gasifier, is meant a reactor allowing the transformation of a         solid fuel into a gas fuel.     -   By reactor, is meant an enclosure which allows thermochemical         transformations.     -   By sole, is meant a surface on which rests the organic material         to be treated, consisting of openworked elements such as grids.     -   By airspace, is meant a single empty zone above the bed where         the oxidation reactions take place.     -   By biomass, is meant all carbonaceous products directly or         indirectly stemming from photosynthesis and notably but not in a         limiting way, plants, animals, diverse organic waste, comprising         domestic refuse, water sewage sludges, etc.

Generally, it is known that many solutions have already been proposed for the purpose of beneficiating biomass and organic byproducts.

Thus, notably, French patent FR No. 78 31356 describes a gas producer with a fixed bed comprising a horizontal treatment chamber in which the materials to be treated are introduced through one of the ends, and then are driven inside the chamber by a driving device up to a discharge aperture formed in the lower portion of the wall of the chamber at its second end. Between both ends of the chamber, the wall comprises two outlets spaced apart from each other, i.e.:

-   -   a first outlet located on the side of the first end of the         chamber, and     -   a second outlet which forms the gas outlet of the gas producer.

The first outlet is connected through a recycling circuit to an injection nozzle, located below a pre-heated air injector, so that the hot gases produced by the reaction of the recycled gases and of the pre-heated air are injected towards the first end of the chamber, at a level corresponding to that of the base of the slope formed in front of the material contained in the chamber. Consequently, the material particles which are the closest to the aperture are attacked by the hottest gases (about 1,200° C.) so that the ashes are rejected after the carbon has been totally gasified.

This solution notably has the advantage of reducing the drying and pyrolysis times by the forced hot gas circulation generated by the recycling. Further, the use of hot gases is optimized in order to obtain complete and rapid gasification.

Nevertheless, the drawback of the solution as described in this document consists in that it does not comprise a self-adaptive structure capable of optimizing the gasification process according to the flow rate of the treated material or, conversely, according to the required power output, and this for variable flow rates or powers in relatively wide ranges.

Patent FR No. 80 16854 proposes improving the treatment method as described earlier by having a heated-up gas flow resulting from recycling pass through the material to be treated, no longer axially as earlier, but transversely relatively to the longitudinal direction of progression of the materials during the treatment in the chamber. More specifically, according to this method, the treatment chamber comprises a succession of treatment modules, each comprising its own recycling, air admission and combustible gas extraction means. This is therefore a relatively expensive solution. Moreover, the goal at which this solution is aimed, is obtaining an optimization of the flow characteristics of the gases through the crossed material layer and not adapting the operation of the treatment chamber according to the material flow rate and/or the required power output, because of the presence of several oxidation zones and of a single gasification zone.

The object of patent application US 2007.0006528 is a method and a corresponding device allowing transformation of a solid carbonaceous material into a combustible gas with low tar content, this transformation being carried out in a vertical gasification chamber-reactor. This method notably comprises the following main steps:

-   -   introduction of the carbonaceous material into the chamber;     -   transformation of a first portion of the carbonaceous material         into coal in a flame pyrolysis zone;     -   control of a plurality of temperatures along the chamber by         injecting an oxidizing gas at several levels in the gasification         chamber;     -   controlling an amount of oxidizing gas injected from one of said         levels;     -   modification of the location of the flame pyrolysis zone by         increasing or by reducing an amount of oxidizing gas injected         upstream or downstream from the pyrolysis zone;     -   controlling the porosity of the coal and of a second portion of         the carbonaceous material in the gasification chamber-reactor by         applying at least one force to the chamber;     -   transformation of the coal and of the second portion of the         carbonaceous material into a low tar content combustible gas,         inside the gasification chamber-reactor.

The object of patent application FR 2 263 290, as for it, is a method and installation for treating bituminous shales and asphaltic limestones by pyrogenation. This method mainly consists in a treatment in a vertical gas producing oven of rocks containing exploitable organic material and notably bituminous shales, in which these rocks are first submitted to a pyrogenation reaction and then to a gasification reaction. This method is characterized in that:

-   -   the diverse required gases are injected into the zone where the         gasification reaction is triggered at different levels, the         operation for dosing and mixing these gases being automatically         adjusted in devices located outside the oven, and in that     -   after its extraction from the reaction zone and before exiting         the oven, the mineral residue is cooled in the lower portion of         the oven by means of a gas in a closed circuit with heat         recovery.

It is found that the object of both patent applications US 2007/0006528 and FR 2 263 290 is a reactor and an oven, the bed of which is vertical, with which it is not possible to obtain perfect homogenization of the temperature inside the bed and control of the flow rate. Further, the flow of material to be treated in the device, object of patent application US 2007/0006528, may be hindered by the injection ramps.

Therefore more particularly, the object of the invention is a gasification method with which the operation of the treatment chamber may notably be adapted according to the nature of the material and/or to the required power output, by means of functional adaptation of the treatment chamber and this without any significant physical modifications, and without increasing significantly the cost of the installation.

This method involves an installation which comprises a reactor comprising a treatment chamber in which the materials to be treated successively pass through a drying/pyrolysis zone of variable dimensions in which pyrolysis gas extraction is carried out, and then through a gasification zone of variable dimensions in which synthesis gas extraction is carried out, the pyrolysis gas extracted in the drying/pyrolysis zone being injected into the airspace of the reactor with an oxidizing gas, so as to generate an exothermic oxidation reaction providing the energy required for pyrolysis and gasification reactions.

According to the invention, the dimensions and/or the position of the drying/pyrolysis and gasification zones are adjusted according to the amounts of material to be treated introduced into the treatment chamber, to their nature, notably on the their grain size and to their hygrometry level and/or to the power output needs, and in that the combustible material substantially circulates horizontally by means of a pusher or the like allowing the combustible material to advance from upstream to downstream from the reactor.

Moreover, the treatment chamber may comprise between the drying/pyrolysis zone and the gasification zone, a mixed zone in which either extraction of pyrolysis gas or extraction of synthesis gas may be carried out, the type of extraction carried out in this zone being determined according to the amounts of materials introduced into the treatment chamber, to the nature of this material and/or to the power output needs.

Further, at least one of the aforesaid zones may comprise several successive controllable gas extraction areas, the variation of the dimensions and/or of the position of said zones being obtained by partial or total deactivation of said areas.

The invention also relates to a gasification installation allowing the application of the method defined earlier, this installation comprising a fixed a bed reactor which comprises a treatment chamber comprising a sole on which the bed of combustible material substantially circulates horizontally, said bed being divided into at least three zones, i.e.:

-   -   a first upstream zone where only one drying/pyrolysis process is         carried out, this zone being connected to pyrolysis gas         extraction means with variable flow rate, these extraction means         being connected to a common circuit for extracting pyrolysis gas         connected to a burner supplied with oxidizing gas such as air or         oxygen and located so as to generate an exothermic oxidation         reaction in the airspace of the chamber of the reactor, the         latter providing the energy required for the pyrolysis,         gasification and degradation reactions of tars or other organic         molecules contained in the pyrolysis gases,     -   a last zone where only one gasification process is carried out         resulting from a reduction phase produced upon passage of the         gas generated by the oxidation reaction through the carbonized         bed during the drying/pyrolysis process, this downstream zone         being equipped with means for extracting at a variable flow rate         the synthesis gas obtained by this gasification process,         connected to a common circuit for extracting synthesis gases,     -   a multifunctional zone located between the first and second         zone, this multifunctional zone may totally or partly be a         drying/pyrolysis zone, and/or totally or partly be a         gasification zone and/or totally or partly be deactivated, and         is connected to extraction means connected to the common circuit         for extracting pyrolysis gases via a circuit with adjustable         flow rate on the one hand, and to the common circuit for         extracting synthesis gases via a circuit with adjustable flow         rate on the other hand.

Thus, when an extraction means or a circuit with variable flow rate is closed, the zone of the treatment chamber corresponding to this extraction means or to this circuit is made at least partly inactive. It therefore becomes possible to distribute the active and inactive zones of the treatment chamber according to the nature of the material to be treated, to the amounts of material to be treated and/or to the desired power output. The presence of the multifunctional intermediate zone in which the extraction means may be connected to the pyrolysis gas extraction circuit or to the synthesis gas extraction circuit notably allows axial displacement of the location where the separation is carried out, between the pyrolysis gas extraction zone and the synthesis gas extraction zone.

Advantageously:

-   -   the circulation rate of the combustible material to be treated         inside the treatment chamber may be variable and may be adjusted         according to the amounts of material to be treated and/or to the         power output needs,     -   the relative flow rates of the oxidizer injected into the         reactor and of extraction of the gasification combustible gas         may be adjusted so as to maintain the reactor depressurized,     -   the produced power output may be controlled by the combustible         material supply, the displacement rate of the combustible         material by means of a piston or the like, by the flow rate and         the quality of the injected oxidizer, the volume of the         pyrolysis zone, the recirculation flow rate, the volume of the         gasification zone, the extraction flow rate of gasification gas.

Moreover, with the purpose of improving the energy yield of the gasification installation described earlier, it is desirable to provide at the outlet of the gasifier, a system for treating high temperature gas loaded with many residual bothersome elements, notably tars or other organic molecules, this system comprises at least one piece of equipment notably having the purpose:

-   -   of cooling the synthesis gas which is extracted at a temperature         which may range from 400° C. to 650° C. in order to bring it to         a temperature below 150° C. allowing application of a scrubbing         process (which is generally performed at a moderate         temperature),     -   of reducing or even removing the tar content,     -   of recovering the substantial heat of the synthesis gas thereby         increasing the thermal yield of the gasification system.

This treatment equipment (tar condenser) is preferably designed so as to carry out wet treatment of the gas under ambient conditions, with a cooling step which is performed on a gas-water tube exchanger with which the substantial heat of the synthesis gas may be recovered and the tars may be separated from the gas. This three-fluid exchanger may comprise a plurality of vertical tubes in which the synthesis gas circulates as well as means with which a falling film formed by circulation of oil may be generated in the tubes. This falling film has the effect of trapping the dusts and tars thereby preventing fouling of the tubes. By cyclically drawing off oil, it is possible to maintain its quality by deconcentrating it by adding new fluid.

An embodiment of such an installation will be described hereafter, as a non-limiting example, with reference to the appended drawings wherein:

FIG. 1 is a schematic illustration of a fixed bed gasification installation;

FIG. 2 is an elevational view with partial cut-aways of a three-fluid exchanger-condenser device which may be used in the installation illustrated in FIG. 1.

In this example, the gasification installation involves a fixed bed reactor 1 of tubular shape, for example with a circular or polygonal section, comprising a treatment chamber 8. This reactor 1 and this chamber 8 are connected at one of their ends (upstream) to a combustible material supply system 2 and comprise at the other downstream end a system 3 for extracting ashes.

Here, the supply system 2 comprises a worm-screw conveyor 4 or any equivalent device located in the storage area 5 of the combustible material. This conveyor 4 delivers onto a belt conveyor 6 which feeds a vertical supply air-lock 7 which opens out inside the treatment chamber 8 of the reactor 1 at right angles to a discharge area 9 of the bed poured into said chamber 8. The material delivered by the air-lock 7 onto this discharge area 9 is pushed back towards the inside of the chamber 8 by a pusher 10 with an alternating movement.

Beyond the discharge area 9, the sole of the treatment chamber 8 is formed by a succession of gas extraction areas on which the bed of combustible material may circulate under the driving effect of the pusher 10. This sole comprises one or more grids 11-15 covering portions under each of which a hopper T₁-T₅ is positioned, the lower portion of which is provided with an obturator or register 16-20 intended for discharging fine material particles passing through the grid(s) 11-15.

According to this embodiment, the sole successively comprises two pyrolysis gas extraction areas (grids 11 and 12), two mixed or polyvalent extraction areas (grids 13 and 14) and an area for extracting synthesis gases (grid 15).

The hoppers T₁-T₄ are each connected to the suction inlet of a pyrolysis gas extraction circuit 21 and of a turbine 23, via suction conduits 24, 25, 26, 27, equipped with valves 28, 29, 30, 31.

Also, the hoppers T₃, T₄, T₅ are connected to the suction inlet of a synthesis gas extraction circuit 37 via suction conduits 31′, 32, 33 equipped with valves 34, 35, 36. The extraction circuit 37 successively comprises the primary of a gas/air heat exchanger 38 and, optionally, a scrubber system for the gases 39. It is connected to the suction inlet of a turbine 40, the outlet of which is for example connected to a synthesis gas distribution network.

The downstream end of the treatment chamber 8 is provided with a well 41 for extracting ashes, the lower end of which is immersed in water 42 contained in a tank 43 for recovering ashes, which extends under the treatment chamber 8.

Also, the obturators (or registers) 16-20 are connected to sleeves M which are immersed in the water of the tank 43.

The particles of ashes or of combustible materials collected by the tank are carried away by a conveyor 44 and poured at a height above the water level of the tank 43 into an area 45 for storing ashes and residues.

The turbine 23 of the pyrolysis gas extraction circuit is connected through its outlet to a burner 50 which injects into the airspace of the treatment chamber 8 a gas mixture comprising the pyrolysis gas as well as an oxidizer which may consist in preheated air from a circuit 46 passing through the secondary of the heat exchanger 38 and from a turbine 47 or in oxygen from a distribution circuit 48 controlled by a valve 49.

The starting of the installation is moreover ensured by means of a burner B using natural gas from a circuit C controlled by a solenoid valve E. This burner B is maintained in operation until the reaction temperature is reached.

Inside the treatment chamber 8, above the extraction areas 11, 12 (and 13, 14 insofar that the valves 30 and 31 are open and the valves 34 and 35 are closed), there exists a drying/pyrolysis zone in which the oxidized gas flow from the burner 50 and circulating in the airspace of the chamber 8 passes through the bed of material lying on the sole (grids 11-14) while causing by their supply of energy, drying of the material and the pyrolysis reaction, the tars contained in the pyrolysis gases being degraded during the oxidation reaction which is carried out in the airspace of the chamber 8 at a high temperature.

In the first portion of the treatment chamber (drying and pyrolysis zone), the gases are extracted at a temperature of the order of 500° C.-700° C.

In the second portion of the reactor, when the gas from the oxidation passes through the carbonized bed during the pyrolysis phase, a reduction phase occurs and the gas is extracted through the suction conduit 33 and the suction conduits 31′ and 32 insofar that the valves 34 and 35 are open.

It therefore appears that the dimensions and the position of the gas extraction zones (pyrolysis and gasification) may be modified depending on the (open or closed) condition of the valves 28-31 and 34-36.

Also, it is possible to adjust the extraction flow rates in these zones. It is therefore possible to generate active or inactive zones of the bed of material according to the power output need.

More practically, variation of the power output of such an installation is achievable by a combination of the following actions:

-   -   varying the supply flow rate of material to be treated by acting         on the actuation rate of the pusher and on the cycle for         supplying material to be treated,     -   varying the dwelling time in the drying and pyrolysis zone by         adjusting the dimension of this zone by closing or opening the         valves 28, 29, 30 and 31,     -   varying the recycled pyrolysis gas flow rate, by adjustment of         the turbine of the pyrolysis gas extraction circuit,     -   varying the dwelling time of the material to be treated in the         gasification zone by adjusting the dimension of this zone by         closing or opening the valves 34, 35, 36,     -   varying the synthesis gas flow rate by adjustment of the turbine         rate of the synthesis gas extraction circuit.

These actions are here controlled by a processor P which controls the rate of supply of the airlock with combustible material, the condition of the registers 16-19 and of the valves 28-31 and 34-36, the speed of rotation of the turbines 23, 40, 47, the speed of rotation of the motor driving the conveyor 44 which ensures extraction of the ashes and of the residues.

This processor is moreover connected to detectors (notably a temperature detector DT and a pressure detector DP) with which the different parameters of the installation may be measured in order to provide the controls and safety measures.

Moreover, for a given power, the operation of the installation is ensured by three control loops:

-   -   a control loop for the depressurization in the reaction chamber,         by action on the synthesis gas extraction flow rate. This action         may be carried out by adjusting the speed of the turbine or by         acting on the valves; this control loop is inevitable for safety         issues.     -   a control loop for the temperature of the oven by acting on the         flow rate of injected oxidizer (air or oxygen) into the burner.         This action may be carried out by adjusting the speed of the         turbine for the oxidizing gas.     -   a control loop for the temperature of the pyrolysis gases by         acting on the recirculation flow rate of the pyrolysis gases.         This action may be carried by adjusting the speed of the         turbine; the temperature of the pyrolysis gas reflects the         temperature in the reactor and the pyrolysis quality.

Further, many adjustable parameters may directly contribute to the performance of the installation, i.e., notably:

-   -   the tilt angle of the sole of the reaction chamber; although the         sole is substantially horizontal in the example described         earlier, it is of course possible to provide a sole having a         predetermined tilt,     -   the progression rate of the material to be treated on the sole,     -   the recirculation gas rate in the pyrolysis bed,     -   the gas rate in the gasification bed,     -   the flow rate and the nature of the oxidizing gas,     -   the temperature in the oxidation zone of the reactor,     -   the surface area of the effective zones of the sole,     -   the positioning and the size of the pyrolysis zone,     -   the positioning and the size of the gasification zone;

By means of the arrangements described earlier, the gasification installation has the following advantages:

-   -   The possibility of varying (or regulating) the capacity or the         power of the installation without having to change the structure         and/or the physical dimensions of the installation; this power         variation is achievable over a significant range. A gas producer         designed for an average power of 1MW may have its power vary         from several hundred kW to several MW.     -   The power changes may be carried out instantaneously and very         easily (total automation) without any consequence on the quality         of the synthesis gas. With the high recycling rate, it is         possible to momentarily operate the system in a standby mode         without any negative effect upon changing over to the rated         output mode. It is sufficient to slow down the inflows of         oxidizer, which allows high reactivity and if the situation         persists, to slow down the inflow of solid. This control         capability is essential because for certain applications         (cogeneration or pure thermics), the variations of the         instantaneous heating value have to be compensated by an         inversely proportional variation of flow rate in order to         maintain constant power. For other uses, the power demand has to         be able to be followed instantaneously.     -   The polyvalence of combustible materials: progression of the         solid in the reactor is no longer by gravity, the density of the         material is no longer a limiting selection criterion, which         opens new possibilities for using varied products (in nature and         in packaging) and so that an operation with increased         reliability may be foreseen.     -   The absence of tar in the gas: the recirculation of the gas         described earlier has another very favorable consequence in         addition to the thermal homogenization effect and to the         mechanical diffusion effect. The multiple successive crossings         of the bed allow total conversion of carbon into CO and CO₂ with         an excellent CO/CO₂ ratio and of hydrogen into H₂ and H₂O with         there also an excellent H₂/H₂O ratio. The pyroligneous juices         commonly called tars which are more or less long hydrocarbon         chains which subsist because of incomplete reactions, are         gradually destroyed as they form in this type of gasifier. This         is a crucial point for using synthesis gas in cogeneration         groups but even more for use in hydrogen chemistry (fuel cell or         conversion into biofuel).     -   The possibility of using an oxygen oxidizer: if the intention is         to produce a gas with a better instantaneous heating value per         unit mass, its inert nitrogen fraction (50% by volume in air         gas) has to be removed. The latter is mainly brought by the         oxidizing air. By gasifying with oxygen, it is possible to         reduce by half the gas flow rate while keeping endogenous         energy. In other words, the instantaneous heating value of the         gas is doubled by reducing by half the substantial thermal         heating loss.     -   A risk of limited blocking of the mechanism for moving the         combustible material to be treated forwards. Anyhow, the         optional curative action is clearly simplified. Internal         interventions are accomplished by opening a front door upon         standstill of course, but without complete emptying of the         reactor as in the prior solutions.

In the example illustrated in FIG. 2, the gas scrubbing system 39 may consist of a tar condenser comprising a vertical tubular column CT closed at both of its ends and the internal volume of which comprises from top to bottom:

-   -   a gas admission chamber 51 into which a gas admission conduit 52         opens out radially.     -   an exchanger 53 delimited by two radial axially spaced         partitions 54, 55, crossed by a plurality of vertical tubes 56         which extend axially between said partitions 54, 55. The volume         57 delimited by the tubes 56, both partitions 54, 55 and the         wall of the CT column is filled with water which circulates         countercurrently between a water inflow conduit 58 located in a         lower portion and a water outflow conduit 58′ located in an         upper portion.     -   a gas outflow chamber 59 into which a gas outflow conduit 60         opens out radially.     -   an oil reserve 61 in which is positioned a double wall in which         runs tubing or any other coil-shaped device 62, the purpose of         which is to cool the oil and to preheat the water, and one of         the ends 63 of which is connected to the water inlet 58 while         the other end is connected to a “cold” water supply circuit 64.         The bottom of the column CT which forms the bottom of the oil         reserve 61 has a conical shape at the centre of which is         positioned an orifice connected to an oil purge pipe 65.

In this device, the synthesis gas forms the fluid to be treated. Water is used as a main heat transfer fluid which absorbs part of the heat released by the gas. The oil which is used for capturing the tars also plays the role of a secondary transfer fluid ensuring preheating of the water.

The gas which enters the admission chamber 51 at a relatively high temperature, flows through the exchanger 53 from top to bottom inside the tube 56 while cooling upon contacting the latter.

After having been preheated in the coil 62, the water passes through the exchanger 53 from bottom to top while heating up upon contacting the tubes 56. The oil which is supplied in the admission chamber 51 (by a circuit not shown) enters the tubes 56 by overflow and forms films falling along the inner walls of the tubes 56 before finally reaching the reserve 61. The substantial heat of the gas is transferred to the water by passing through oil films and the walls of the tubes 56. The tars present in the gas are captured by the oil films during the direct tar/oil contact. The oil present in the reserve 61 may be regularly drawn off by means of a purge pipe 65. 

1. A method for variable power gasification of combustible materials with an installation which comprises a reactor comprising a treatment chamber wherein the materials to be treated successively pass through a drying/pyrolysis zone with variable dimensions in which pyrolysis gas extraction is carried out, and then through a gasification zone with variable dimensions in which synthesis gas extraction is carried out, the pyrolysis gas extracted in the drying/pyrolysis zone being injected into the airspace of the treatment chamber with an oxidizing gas, so as to generate an exothermic oxidation reaction providing the energy required for pyrolysis and gasification reactions, wherein the dimensions and/or the position of the drying/pyrolysis and gasification zones are adjusted according to the amounts of material to be treated, introduced into the treatment chamber, to their nature and/or power output requirements, in that the treatment chamber comprises a single oxidation zone in the airspace of the reactor, and wherein the combustible material substantially circulates horizontally by means of a pusher or the like allowing the combustible material to advance from upstream to downstream from the reactor, this reactor being positioned along a substantially horizontal axis.
 2. The method according to claim 1, wherein the treatment chamber comprises between the drying/pyrolysis zone and the gasification zone, a mixed multifunctional zone in which either pyrolysis gas extraction or synthesis gas extraction may be carried out, the type of extraction carried out in this zone being determined according to the amounts of materials introduced into the treatment chamber, to the nature of this material and/or to the power output needs.
 3. The method according to claim 2, wherein at least one of the aforesaid zones comprises several controllable successive gas extraction areas, and wherein the variation of the dimensions and/or of the position of said zones is obtained by partial or total deactivation of said areas.
 4. The method according to claim 3, wherein the temperature of the gasification gases is controlled by acting on the flow rate of oxidizing gas injected into said chamber.
 5. The method according to claim 3, wherein the temperature of the pyrolysis gases is controlled by acting on the flow rate of the pyrolysis gases injected into the treatment chamber.
 6. The method according to claim 3, wherein the relative flow rates of the oxidizer injected into the reactor and of extraction of the gasification fuel gas maintains the reactor depressurized.
 7. The method according to claim 3, wherein the produced power output is controlled by the supply of combustible material, the displacement rate of the combustible material by means of a piston or the like, the flow rate and quality of the injected oxidizer, the volume of the pyrolysis zone, the recirculation flow rate, the volume of the gasification zone, the flow rate of extraction of the gasification gas.
 8. The method according to claim 2, wherein the synthesis gas is subject to a scrubbing treatment with recovery of the substantial heat of said gas.
 9. The method according to claim 8, wherein the aforesaid scrubbing is carried out by means of a falling oil film generated in the exchanger tubes in which said gas flows.
 10. An installation for applying the method comprising a fixed bed reactor which comprises a treatment chamber, this reactor and this chamber being connected at one of their ends to a combustible material supply system comprise at their other end a system for extracting ashes and, this chamber comprising three regions corresponding to the three main phases of the treatment, i.e.: a drying/pyrolysis region located in a first portion of the combustible material bed, a gasification region located in the second portion of the bed of the fuel and an oxidation region occupying the airspace located above the bed, wherein the chamber comprises a substantially horizontal sole surmounted by a bed divided into at least three zones, i.e.: a first upstream zone with variable dimensions where only a drying/pyrolysis process is carried out, this zone being connected to means for extracting the pyrolysis gas with variable flow rate, these extraction means being connected to a common pyrolysis gas extraction circuit connected to a burner supplied with an oxidizing gas such as air or oxygen and positioned so as to generate an exothermic oxidation reaction in the airspace of the chamber, which provides the energy required for the pyrolysis, gasification and degradation reactions of the tars or other organic molecules contained in the pyrolysis gases, a last zone with variable dimensions where only a gasification process is carried out which results from a reduction phase produced during the passage of the gas generated by the oxidation reaction through the carbonized bed during the drying/pyrolysis process, this downstream zone being equipped with means for extracting with a variable flow rate the synthesis gas obtained by this gasification process, connected to a common circuit for extracting synthesis gases, a multifunctional zone with variable dimensions located between the first and the last zone, this multifunctional zone may totally or partly be a drying/pyrolysis zone and/or totally or partly be a gasification zone, and/or totally or partly be a deactivated zone, and is connected to extraction means connected to the common pyrolysis gas extraction circuit via a circuit with adjustable flow rate on the one hand, and to the common synthesis gas extraction circuit via a circuit with adjustable flow rate on the other hand.
 11. The installation according to claim 10, wherein the supply system comprises a supply airlock which delivers the material to be treated to the inside of the treatment chamber on a discharge area of a pusher with an alternating movement.
 12. The installation according to claim 11, wherein the aforesaid extraction areas each comprise a grid on which the material bed may circulate and under which a hopper is positioned, the lower portion of which is provided with an obturator connected to a sleeve immersed in the water of a tank, at least one synthesis and/or pyrolysis gas extraction circuit opening inside the hopper and controlled by valves.
 13. The installation according to claim 12, wherein the aforesaid pyrolysis gas extraction circuit comprises a turbine which delivers into the aforesaid burner.
 14. The installation according to claim 13, wherein oxidizer is delivered by a circuit passing through the secondary of a heat exchanger, the primary of which is mounted in the circuit for extracting the synthesis gas.
 15. The installation according to claim 14, wherein the treatment chamber comprises a system for extracting ashes comprising a well, the lower end of which is immersed in the water contained in a tank for recovering ashes.
 16. The installation according to claim 15, wherein the aforesaid sole is tilted relatively to the horizontal.
 17. The installation according to claim 16, comprising a gas scrubbing system comprising i.a. a three-fluid exchanger inside which the gas circulates in vertical tubes inside which oil entering by overflow forms films falling along the inner walls of said tubes before finally reaching an oil reserve, the substantial heat of the gas being transferred to the water by passing through the oil films and the walls of the tubes.
 18. The installation according to claim 17, wherein before reaching the exchanger the water circulates in a coil-shaped circuit positioned in the aforesaid reserve. 